Method and system for transmission of seismic data

ABSTRACT

The transmission method utilizes multiple seismic acquisition units within an array as intermediate short range radio receivers/transmitters to pass collected seismic data in relay fashion back to a control station. Any one seismic unit in the array is capable of transmitting radio signals to several other seismic units positioned within radio range of the transmitting unit, thus allowing the system to select an optimal transmission path. Utilizing an array of seismic units permits transmission routes back to a control station to be varied as needed. In transmissions from the most remote seismic unit to the control station, each unit within a string receives seismic data from other units and transmits the received seismic data along with the receiving unit&#39;s locally stored seismic data. Preferably, as a transmission is passed along a chain, it is bounced between seismic units so as to be relayed by each unit in the array.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to seismic data acquisition, and moreparticularly to a method and system for transmitting data betweenmultiple remote stations in an array and a data collection stationutilizing a linked relay system to communicate therebetween permittingtransmission paths to be altered.

2. Description of the Prior Art

Seismic exploration generally utilizes a seismic energy source togenerate an acoustic signal that propagates into the earth and ispartially reflected by subsurface seismic reflectors (i.e., interfacesbetween subsurface lithologic or fluid layers characterized by differentelastic properties). The reflected signals are detected and recorded byseismic units having receivers or geophones located at or near thesurface of the earth, thereby generating a seismic survey of thesubsurface. The recorded signals, or seismic energy data, can then beprocessed to yield information relating to the lithologic subsurfaceformations, identifying such features, as, for example, lithologicsubsurface formation boundaries.

Typically, the seismic units or stations are laid out in an array,wherein the array consists of a line of stations each having at leastone geophone attached thereto in order to record data from the seismiccross-section below the array. For data over a larger area and forthree-dimensional representations of a formation, multiple lines ofstations may be set out side-by-side, such that a grid of receivers isformed. Often, the stations and their geophones are remotely located orspread apart. In land seismic surveys for example, hundreds to thousandsof geophones may be deployed in a spatially diverse manner, such as atypical grid configuration where each line of stations extends for 5000meters with stations spaced every 25 meters and the successive stationlines are spaced 200 meters apart.

Various seismic data transmission systems are used to connect remoteseismic acquisition units to a control station. Generally, the seismicstations are controlled from a central location that transmits controlsignals to the stations and collects seismic and other data back fromthe stations. Alternatively, the seismic stations may transmit data backto an intermediate data collection station such as a concentrator, wherethe data is recorded and stored until retrieved. Whichever the case, thevarious stations are most commonly hard wired to one another utilizingdata telemetry cable. Other systems use wireless methods for control anddata transmission so that the individual stations are not connected toeach other. Still other systems temporarily store the data at eachstation until the data is extracted.

In the case of wired stations, typically several geophones are connectedin a parallel-series combination on a single twisted pair of wires toform a single receiver group or channel for a station. During the datacollection process, the output from each channel is digitized andrecorded by the station for subsequent analysis. In turn, stations areusually connected to cables used to communicate with and transport thecollected data to recorders located at either a control station or aconcentrator station.

In the case of wireless seismic units, each unit communicates witheither a central control station or concentrator via radiotransmissions. Transmissions are made either directly between eachseismic unit and the control station or directly between each seismicunit and the concentrator. To the extent the transmissions are highpower, long-range signals, such as between a seismic acquisition unitand a central control station, the transmissions generally require alicense from the local governing authority. Units capable of suchtransmissions also have higher power requirements and thus requirelarger battery packages. To the extent the seismic acquisition unitstransmit to a concentrator station utilizing a low power, short-rangesignal, the transmitting and receiving units must typically have a lineof site therebetween.

Illustrative of the prior art is U.S. Pat. No. 6,070,129 which teaches amethod and apparatus for transmitting seismic data to a remotecollection station. Specifically, an acquisition unit having a geophoneattached thereto communicates with a central station either directly byradio channels, or optionally, by means of an intermediate station. Tothe extent a large number of acquisition units are utilized, the patentteaches that each a plurality of intermediate stations may also beutilized, wherein each intermediate station directly communicates with aportion of the acquisition units. Intermediate stations may function asdata concentrators and may also be utilized to control various tasksexecuted by their respective groups of acquisition units. Whether datais transmitted directly between an acquisition unit and the centralstation or directly between an acquisition unit and an intermediatestation, the transmitting system accumulates seismic data, distributesthe data over successive transmission windows and discontinuouslytransmits the data during successive transmissions in order to lessenvariation in seismic data flow.

Similarly, U.S. Pat. No. 6,219,620 teaches a seismic data acquisitionsystem using wireless telemetry, in which a large number of remoteseismic acquisition units are grouped together into a plurality of cellsand each acquisition unit within a cell communicates directly with acell access node, i.e., a concentrator, which in turn communicates witha central control unit. This patent teaches that in order to avoidoverlap between transmitting seismic units within adjacent cells,adjacent cells utilize different frequencies for communication betweenunits and their respective cell access nodes. In otherwords, adjacentcells operate at different frequencies so that a particular acquisitionunit is only capable of transmitting to the cell access node assigned toits cell.

One drawback to the aforementioned seismic transmission systems of theprior art is that the failure of any one intermediate transmissionstation or cell access node will prevent communication with a pluralityof seismic acquisition units. Furthermore, to the extent an individualunit is prevented from transmitting back to its respective cell accessnode due to factors external to the unit, the participation andoperation of that unit within the array is lost. For example, a unit maylose radio contact with an access point due to a weak signal, weatherconditions, topography, interference from other electrical devicesoperating in the vicinity of the unit, disturbance of the unit'sdeployment position or the presence of a physical structure in the lineof site between the unit and the access point.

Thus, it would be desirable to provide a communication system for aseismic survey array that has flexibility in transmitting signals anddata to and from remote seismic units and a control and/or datacollection station. The system should be capable of communicationbetween functional seismic units even if one or more intermediatestations fail to operate properly. In addition, the system should becapable of communication between functional seismic units even if achange in environmental or physical conditions inhibits or prevents adirect transmission between a remote unit and its control station.

SUMMARY OF THE INVENTION

The method according to the invention transmits radio signals betweenindividual seismic acquisition units in an array, such that thetransmissions can be passed in a relay chain through the array ofseismic units. Multiple seismic acquisition units within the array arecapable of passing transmissions to multiple other seismic units. Morespecifically, any one seismic acquisition unit in the array is capableof transmitting radio signals to several other seismic acquisition unitspositioned within radio range of the transmitting seismic acquisitionunit. A network of radio-linked seismic acquisition units such as thispermits seismic data transmission routes back to a control station to bevaried as desired or needed. In other words, the transmission pathutilized to transmit data from the individual seismic acquisition unitsin an array back to a control station may be altered. In transmissionsup the chain, i.e., from the most remote seismic acquisition unit to thecontrol station, each unit receives seismic data from a seismic unit“down” the chain and transmits the received seismic data up the chainalong with receiving unit's locally stored seismic data. Preferably, asa transmission moves up the chain, it is bounced between seismicacquisition units so as to be relayed by each unit in the array. Thespecific transmission path, i.e., the chain of units, for any giventransmission may vary between transmissions depending on overall systemrequirements. Control signals and the like can be passed back down thechain along the same or a different transmission path.

The transmitted signal strength can be altered to adjust thetransmission range for a transmitting seismic unit, such that number ofpotential receiving seismic acquisition units can be controlled. In oneembodiment, each seismic acquisition unit is omni-directional in itstransmission and is capable of linking to all units within a 360° rangearound the transmitting unit. Alternatively, a transmitting seismic unitmay utilize a directional antenna such that transmissions are made onlyto one or more seismic acquisition units in a limited or singledirection or more limited range of transmission.

Preferably the individual seismic acquisition units are wireless andrequire no external cabling for data transmission or unit control. Suchunits may contain a battery, a short-range radio transmitter/receiver, alocal clock, limited local memory, a processor and a geophone package.In one embodiment, each unit may include a short-range radiotransmission antenna molded or otherwise integrated into the casing ofthe unit. In another embodiment, each unit may include external spikesthat are used not only to couple the unit to the earth, but also as aconductive conduit through which the unit's batteries can be recharged.

At least one and preferably a plurality of seismic acquisition units inthe network are located in the proximity of the control station so thatthe network can utilize short-range radio frequency to transmit seismicdata all the way back to the control station. In another embodiment ofthe invention, the control station is remotely located from the seismicunits and one or more concentrators are located in the proximity of theseismic acquisition units of the network so that the network can utilizeshort-range radio frequency to transmit seismic data to theconcentrators. The concentrators, in-turn, can store the seismic dataand/or transmit it back as desired to a control station.

Such a concentrator may include a long range transmitter/receiver forcommunicating with a control station, a short range transmitter/receiverfor communicating with the seismic acquisition unit network, mass memoryfor long-term storage of the collected seismic data from the network, apower source, a local clock and a processor. In one embodiment, theconcentrators may communicate with the control station via telemetrycable, while communicating with the seismic acquisition network viashort range transmission.

Within the transmission network, there are multiple transmission pathsfrom the most remote unit to the control station/concentrator. Theparticular transmission path to be used for any given transmission willbe determined based on the strength of the signal between communicatingunits, the operational status of a unit and path efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a seismic acquisition array illustratingpossible transmission paths between seismic acquisition unit strings inthe array.

FIG. 2 is a top view of a seismic data transmission path utilizingseismic acquisition units.

FIG. 3 is an elevation view of a seismic acquisition unit of theinvention.

FIG. 4 is a cut-away top view of the unit of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the detailed description of the invention, like numerals are employedto designate like parts throughout. Various items of equipment, such asfasteners, fittings, etc., may be omitted to simplify the description.However, those skilled in the art will realize that such conventionalequipment can be employed as desired.

With reference to FIG. 1, there is shown a seismic data transmissionnetwork 10 of the invention. Transmission network 10 is comprised of aplurality of seismic acquisition units 12 spread out in a seismic array14 and controlled by control station 16. Array 14 is formed of multiplelines 18 of acquisition units 12. Radio transmissions, and inparticular, seismic data, are passed from seismic unit 12 to seismicunit 12 as the transmission is bounced through the network 10 to controlstation 16. In one embodiment of network 10, concentrators 20 aredisposed between array 14 and control station 16. While the inventionwill be described in more detail with references to transmission ofseismic data, those skilled in the art will understand that theinvention encompasses any type of transmissions from a seismic unit,including, without limitation, quality control data.

Each acquisition unit 12 has an omnidirectional transmission range 22and can form a wireless link 23 with multiple acquisition units 12. Asshown, within the transmission range 22 of a unit 12, there are multipleother units 12 capable of receiving the transmission, in essence forminga local area network comprised of acquisition units 12. For example,unit 12 a has an omnidirectional transmission range 22 a. Falling withinthe transmission range 22 a of unit 12 a are seismic acquisition units12 b–12 g. With the flexibility to transmit to multiple acquisitionunits 12 each having the ability to receive and transmit seismic data tomultiple other units 12 within the array 14, each unit 12 within array14 is presented with multiple paths for communicating seismic data backto control station 16. For example, unit 12′ can transmit data back tocontrol station 16 by sending it along path 24, along path 25 or alongsome other path as determined by the requirements of network 10.

In another embodiment, a transmitting seismic unit 12 may utilizedirectional radio antenna or antenna array such that transmissions aresubstantially unidirectional and made only to one or more seismicacquisition units 12 in a limited direction. It is common in the art toutilize phased antenna arrays-an array consisting of two or moreantenna's-to achieve transmission directionality and gain improvement.In these types of antenna arrangement, various adjustable antennaparameters, such as phase, can be altered to control directionality andgain, and hence, transmission range. Thus, for purposes of thisdescription, “unidirectional” means a transmission with a higher gainalong one axis or in a limited direction, whereas “omni-directional”means a transmission with generally the same gain in substantially 360°.This will maintain the flexibility to transmit to multiple units in thedirection the transmitting antenna is pointed, while reducing the numberof path options that need to be processed by the overall system, therebymultiple paths to be transmitted on the same frequency at the same timewithout interfering with one another. In addition, a higher gain in asingle or limited direction can be achieved without the need foradditional power, or alternatively, power requirements can be decreased,and thus battery life extended, while maintaining the same gain as anomnidirectional signal.

In the illustration of FIG. 1, array 14 is shown as being comprised ofthree seismic acquisition unit strings 18 a, 18 b, and 18 c. Each string18 a, 18 b, and 18 c illustrates a different potential transmission pathdefined by wireless links 23 between the units 12 within a string. Thoseskilled in the art will understand that the indicated wireless links 23are for illustrative purposes only and, for purposes of the invention, a“string” 18 of seismic units 12 for a particular transmission path isdefined by the selected transmission path by which data is communicatedfrom one unit 12 to another. Thus, for any given array 14, a “string” ofunits may be constantly changing between transmissions. Such anarrangement permits transmissions to be re-routed in the event of somefailure of a unit 12 within the string. Likewise, transmissions can bere-routed in the event of a weak signal between units 12 or to overcometopographic or other obstacles that could interfere with short range,line of site transmissions. Furthermore, in addition some failure of aunit, it may be desirable to reroute a transmission simply because ofthe operational status of a unit. For example, a unit with lower batterypower may be utilized downstream at the end of a string and avoided as atransmission relay further upstream in order to conserve the unit'sbatteries, i.e., upstream relay units require more power to relay thetransmission because of the cumulative size of the transmissions.

In the event multiple adjacent strings are desired, radio transmissionparameter assignments may be made to minimize interference with othertransmissions and permit reuse of the same transmission parameters. Forexample, string 18 a may transmit data at a first set of radiotransmission parameters while string 18 b may transmit data at a secondset of parameters. Since the transmissions from a sting 18 are shortrange, it may only be necessary for adjacent strings to utilizedifferent transmission parameters. In this regard, the physical seismicunit layout of a portion of array 14 defined as a string 18 maybedependent on the short range transmission capabilities of the seismicunits 12 in the adjacent string. Non-adjacent strings utilizing the samestring are sufficiently spaced apart so as not to interfered with oneanother. In other words, string 18 b is defined such that its width issufficient to ensure that any transmission from a seismic unit 12 fromstring 18 a transmitting with a certain set of radio transmissionparameters will not be received by any seismic unit 12 from string 18 cset to receive transmissions using the same set of radio transmissionparameters. Those skilled in the art will understand that there are manytransmission parameters that can be adjusted in this regard, includingthe non limiting examples of frequencies, time slots, power, methods ofmodulation, directional antenna gain, physical spacing of units andstrings, etc. Of course, interference between adjacent strings, as wellas individual units, may also be minimized by making transmissions indiscreet data packages sent in short transmission bursts.

Furthermore, while three strings 18 are depicted to indicate possibletransmission paths, system 10 can comprise any number of strings. Thenumber of strings for any given group of transmissions is dependent onthe system requirements. For example, rather than multiple strings, eachacquisition unit 12 in an array 14 may be utilized in a singletransmission path such that the entire array 14 might be considered a“sting” for purposes of the description. Those skilled in the art willunderstand that the number of transmission paths and the number ofacquisition units utilized for any given transmission may constantly bein flux to maximize the operation requirements for a particulartransmission or group of transmissions.

In each case, the transmitted signal strength of a seismic unit 12 canbe altered to adjust the transmission range for a transmitting seismicunit such that number of potential receiving seismic acquisition units12 can be controlled.

At least one and preferably a plurality of seismic acquisition units 12in network 10 are proximately located to control station 16 so thatnetwork 10 can utilize short-range radio frequency to transmit seismicdata to control station 16 from the seismic units 12. However, largeamounts of data transmitted to a control station may be difficult tomanage and typically requires high power, long range transmitters. Thus,in one embodiment of the invention, data is accumulated and stored atmultiple, dispersed concentrators 20 remote from control station 16. Byaccumulating seismic data at concentrators 20, the need for radiolicenses and other requirements associated with long range transmissionsmay be avoided. Concentrators 20 are located in the proximity of theseismic acquisition units 12 of the network 10 so that the network 10can utilize low power, short-range radio transmission to transmitseismic data to the concentrators 20. The concentrators 20, in-turn, canstore the seismic data or transmit it back as desired to control station16. In one embodiment, concentrators locally store seismic data buttransmit quality control data received from the acquisition units backto control station 16.

Much like the individual acquisition units 12, each concentrator 20preferably also has a transmission range 26 that encompasses severalseismic acquisition units 12. As within the array 14, transmission ofdata from a string 18 to the accumulator 20 may be made from a pluralityof units 12. For example, accumulator 20 a has an omnidirectionaltransmission range 26 a. Falling within the transmission range 26 a ofaccumulator 20 a are seismic acquisition units 12 h–12 j. As such, anyof acquisition units 12 h–12 j may transmit seismic data from string 18a to accumulator 20 a. Thus, a failure of one of the acquisition units,such as 12 h, would not prevent seismic data from string 18 a from beingpassed up the line. Rather, the transmission path from string 18 a toconcentrator 20 a would simply be rerouted through an operativeacquisition unit, such as units 12i or 12j. Concentrators 20 may also bepositioned so as to be within the short range transmission distance ofadjacent concentrators.

As described above, network 10 can function as either a one-way network,i.e., concentrators 20 are utilized only to receive seismic datatransmitted from array 14, or a two-way network, i.e., concentrators 20transmit command signals out to array 14 in addition to receivingseismic data transmitted from array 14.

In another configuration, seismic data is transmitted back from array 14utilizing the network of linked seismic acquisition units 12, butcontrol signals are transmitted directly to each acquisition unit 12from either the control station 16 or an associated concentrator 20.

In such case, an acquisition unit 12 may be capable of receiving longrange transmissions directly from a distant source with sufficienttransmission power for such communications, i.e., control station 16, anassociated concentrator 20 or radio repeater stations utilized to extendrange, even though the acquisition unit 12 itself is only capable ofshort range hopped transmissions for sending seismic data back to thecontrol station or concentrator. [30] Transmissions to control station16 from accumulators 20 or acquisition units 12 may also include globalpositioning system (“GPS”) or other survey information to establish thelocation of a particular unit 12 for purposes of the shot and forpurposes of retrieval. This is particularly desirable for wireless unitsas described herein since it may be difficult to locate such units uponretrieval. GPS survey information may also be useful in selection of atransmission path within an array as described above.

In operation, a preferred transmission path may be preset in units 12 orpredetermined. Likewise, alternate transmission paths may be preset inunits 12 or predetermined. These preset paths, as well as the number ofpaths required for a particular array 14, are determined based on thevolume of the data to be transmitted, the data transmission rates,signal strength and the number of “real time” radio channels havingdifferent transmission parameters such that the radio transmissionchannels are non-interfering, battery power, location of the unit, etc.

Prior to a transmission or a set of transmissions along a string, abeacon signal may be utilized to verify the preferred transmission pathin much the same way as an ad hoc network or peer to peer networkidentifies systems within the network. Alternatively, rather thantransmitting data utilizing a preset or predetermined path, the beaconsignal may be used to establish a transmission path utilizing the abovedescribed parameters. If a beacon signal is transmitted and thepreferred transmission path is not available, system 10 will search foranother transmission path through the seismic units. In one embodiment,the beacon signal is transmitted and the local units within range send areturn signal acknowledging their receipt of the beacon signal. Once apath is verified or established, as the case may be, the path may be“locked in” for purposes of the particular transmission so that system10 will not continue searching for another path. The beacon signal maybe generated from within the array 14 by the seismic units themselves orinitiated by the control station or concentrator.

A synchronization signal may also be used to synchronize the recordingtime for the units of system 10 by establishing a future time t(0) atwhich trace recording by seismic units 12 is to begin. In contrast, theprior art typically sends out a pulse signal that immediately triggersrecording by each seismic unit at the time it receives the signal suchthat prior art seismic units located closer to the signal source beginrecording earlier than seismic units more remote from the signal source.In a preferred embodiment of the invention, all seismic units 12 may beset to start recording at a specific clock time, such that datatransmitted back through network 10 is time stamped based on thesynchronization shot time. In this regard, all data is time synchronizedregardless of the transmission path utilized by the network or theperiod of time the network takes to transmit the data through thenetwork.

In this same vein, it is also desirable to ascertain the data delayalong the path based on master clock time so that data that is not timestamped can be synchronized with the data from other seismic units. Thedescribed network 10 permits data to be retrieved via radio transmissionin real time or near real time.

While the invention has been described in its broadest sense aspossessing the flexability to alter data tranmission paths, i.e., eachunit has wireless links with multiple other units, in order to conveyacquired seismic data from an array of acquisition units back to acontrol station or concentrator, it is also true that none of the priorart transmission systems utilize seismic data acquisition units asintermediate transmission devices. Thus, one aspect of the invention asillustrated in FIG. 2 is the use of seismic data acquisition units 12themselves, configured in a predetermined string, as intermediatedevices for passing transmissions from a seismic unit in the string to acontrol station. In this regard, a string 40 of seismic units 42 ispredetermined and defined by an outermost unit 42 a and a plurality ofintermediate units 42 b through 42 i. Each unit 42 in string 40 has awireless link 44 within its transmission range 46 only with the unitsdirectly up and directly down the string. For example, sesimic unit 42 gis only capable of communication with sesimic units 42 f and 42 h viatheir respective wireless links 44 because only units 42 f and 42 h arewithin the transmission range 46 of unit 42 g. Upon acquisition of data,unit 42 g will transmit the acquired data up the string to 42 h, alongwith any data received by wireless transmission from 42 f. All sesmicdata from the units 12 comprising string 40 will be conveyed up thestring to control station 16. Control station 16 can likewise utilizethe seismic units 12 to pass control and command signals back down thestring.

As mentioned above, one benefit of the invention is the ability toutilize flexible transmission paths that can be readily changed based onvarious internal and external parameters effecting the network. Thisflexability also renders the network itself much more reliable.Preferably, transmission paths can be established and/or reroutedon-the-fly based on these parameters. Another advantage of the system isthat it utilizes less power in transmitting a signal over a givendistance via multiple short transmissions than would be required of asingle tranmission over the same distance. In other words, because thepower required to transmit a signal decreases as one over the square ofthe tranmission distance, it is much more optimal to transmit a signalin several short hops than it would be to transmit the same signal overthe same distance in a single hop. This is true even of low power, shortrange transmissions. Of course an additional advantage of the system ofthe invention is that it avoids the need to acquire long range radiotranmission licenses. Finally, unlike the prior art, the system of theinvention eliminates the need to physically locate a concentrator orsimilar device in the middle of a seismic array, nor utilize theconcentrator to sort and organize multiple seismic data transmissionsincoming directly from individual seismic acquisition units.

Turning to the individual seismic acquisition units as illustrated inFIGS. 3 and 4, each unit 12 is preferably wireless and requires noexternal cabling for data transmission or unit control. Each unit 12 maycontain a battery 30, a short-range radio transmitter/receiver 31, alocal clock 32, limited local memory 33, and a processor 34 housedwithin a casing 35. A geophone package 36 may be housed within thecasing 35 or externally attached thereto. Any standard short range radiotransmission equipment may be utilized. One non-limiting example beingwireless fidelity (“Wi-Fi”) equipment, where transmission parametersmaybe selected to provide signal carrier modulation schemes such ascomplementary code keying (CCK)/packet binary convolution (PBCC) ordirect sequence spread-spectrum (DSSS) or multi-carrier schemes such asorthogonal frequency division multiplexing (OFDM) and code divisionmultiple access (CDMA). Local memory capacity is preferably limitedsince local seismic data is only retained for a short period of time.Further, because the unit 12 need only transmit a short range signal,power requirements for the unit are minimized in contrast to theincreased power requirements necessary to transmit a stronger signal toa more distant receiving device. By reducing the memory requirements,the transmission requirements and the battery requirements, the overallcost, as well as the physical size and weight, of each unit isminimized.

While each unit may include an antenna, attached via an externalconnector, in one embodiment of the invention, each unit 12 may includea short-range radio transmission antenna 36 molded or otherwiseintegrated into the casing 35 of the unit. This eliminates the need foran external connector. Each unit 12 may also include radio frequencyidentification or similar identification indicia, such as a bar code.Finally, each unit 12 may include a receiver for receiving long rangeradio transmissions directly from a control station or concentrator asdescribed above.

In another embodiment, each unit 12 may include external projections orspikes 37 that are used not only to couple the unit to the earth, butalso as an electrically conductive conduit through which the unit'sinternal batteries 30 can be recharged. Such a configuration minimizesthe need for external connectors which are known in the industry as asource of various problems such as corrosion, leakage, etc. oralternatively, the need to otherwise open the sealed unit. While anyshape, length or number of projections or spikes may be utilized, onepreferred configuration utilizes three spikes that can also be utilizedto couple the unit to the earth. In a three spike configuration, two ofthe spikes are connected to the battery through a relay or similarmechanism. The third spike would be used to control the relay. Duringcharging, the relay would be closed; after charging, the relay would beopen to prevent battery discharge.

Concentrator 20 (not shown) may include a long range radiotransmitter/receiver for communicating with a control station 16, ashort range radio transmitter/receiver for communicating with thenetwork of seismic acquisition units 12, a power source, a local clockand a processor. In one embodiment, concentrator 20 functions simply asan intermediate long range receiver/transmitter to relay short rangetransmissions from the network of seismic units 12 to the controlstation 16. In another embodiment, concentrator 20 is provided with massmemory for storage of seismic data transmitted from the network ofseismic units 12. In either embodiment, concentrator 20 may relaycontrol signals and other transmission from the control station 16 backto the network of seismic units 12. In this same vein, concentrator 20may be disposed to function as a local control station for a network ofseismic units 12. While the preferred embodiment utilizes radiofrequency for transmissions between concentrator 20 and control station16, transmissions therebetween may also occur through various othertransmission vehicles, such as telemetry cable or optic cable.

While certain features and embodiments of the invention have beendescribed in detail herein, it will be readily understood that theinvention encompasses all modifications and enhancements within thescope and spirit of the following claims.

1. A method for seismic data transmission comprising the steps of: A.providing a plurality of seismic acquisition units, wherein each of saidseismic acquisition units is capable of acquiring seismic data,receiving a short range radio transmission and transmitting a shortrange radio transmission; B. utilizing a at least two of said seismicacquisition units to transmit seismic data via short range radiotransmission to another seismic acquisition unit in the array; C.utilizing a at least two of said seismic acquisition units to receiveseismic data via short range radio transmission from another seismicacquisition unit in the array; D. partitioning said plurality of seismicacquisition units into at least two sub-sets of seismic acquisitionunits; and E. using a short range radio transmission technique havingparameters set so that non-interfering radio transmission may beeffected in each sub-set.
 2. The method of claim 1, further comprisingthe steps of partitioning said plurality of seismic acquisition unitsinto a third sub-set, wherein the first and third sub-set of seismicacquisition units are spaced apart from one another by said secondsub-set of seismic acquisition units.
 3. The method of claim 2, furthercomprising the step of assigning transmission parameters so the thirdsub-set of seismic acquisition units have the same short range radiotransmission parameters as that assigned to the first sub-set.
 4. Themethod of claim 1, further comprising the step of utilizing a pluralityof said seismic acquisition units within said first subset to transmitseismic data via short range radio transmission to other seismicacquisition units in the first subset while simultaneously utilizing aplurality of said seismic acquisition units within said second subset totransmit seismic data via short range radio transmission to otherseismic acquisition units in the second subset, wherein eachtransmission is made utilizing the short range radio transmissionparameters assigned to the respective subset.
 5. The method of claim 1,further comprising the step of utilizing a plurality of said seismicacquisition units within said first subset to transmit seismic data viashort range radio transmission to other seismic acquisition units in thefirst subset while simultaneously utilizing a plurality of said seismicacquisition units within said second subset to transmit seismic data viashort range radio transmission to other seismic acquisition units in thesecond subset while simultaneously utilizing a plurality of said seismicacquisition units within said third subset to transmit seismic data viashort range radio transmission to other seismic acquisition units in thethird subset, wherein each transmission is made utilizing the shortrange radio transmission parameters assigned to the respective subset.6. The method of 3, wherein each seismic acquisition unit has a radiotransmission range and the seismic acquisition units within the firstand third subsets are sufficiently spaced apart so as to fall outsidethe transmission range of any seismic acquisition unit within therespective subsets.
 7. The method of 3, wherein each seismic acquisitionunit has a radio transmission range that can be adjusted by adjustingthe transmission parameters so that the first and third sub-sets havetransmission ranges that do not interfere with one another.
 8. Themethod of claim 1 wherein each acquisition unit has a set oftransmission parameters associated therewith and an adjustabletransmission range, the method further comprising the step of adjustingthe transmission range by adjusting the transmission parameters.
 9. Themethod of claim 8, wherein the transmission range is adjusted byadjusting the transmission power.
 10. The method of claim 1, wherein atleast one seismic acquisition unit is capable of receiving short rangeradio transmissions from at least two other seismic acquisition units.11. The method of claim 10, wherein each seismic acquisition unit iscapable of receiving short range radio transmissions from at least twoother seismic acquisition units.
 12. The method of claim 10, whereineach seismic acquisition unit is capable of receiving short range radiotransmissions from at least three other seismic acquisition units.
 13. Amethod for seismic data transmission comprising the steps of: A.providing at least three spaced apart seismic acquisition units deployedin an array, wherein each of said seismic acquisition units is capableof receiving a short range radio transmission and transmitting a shortrange radio transmission; B. providing a receiving station for receivinga short range radio transmission from at least one seismic acquisitionunit within said array; C. subsequent to deployment, identifying atleast two separate transmission paths from a seismic acquisition unit tothe receiving station, wherein a transmission path is defined as a chainof at least two seismic acquisition units and the receiving station,each capable of communicating in series via short range radiotransmission; D. selecting a transmission path from the identifiedtransmission paths based on a set of transmission path criteria; and E.transmitting a signal along said selected transmission path.
 14. Themethod of claim 13, further comprising the step of transmitting a firstsignal along one transmission path and transmitting a second signalalong the other transmission path.
 15. The method of claim 13, whereineach of said seismic acquisition units is capable of acquiring seismicdata.
 16. The method of claim 15, further comprising the step ofacquiring seismic data utilizing said seismic acquisition units.
 17. Themethod of claim 16, wherein the transmitted signal received by thereceiving station includes seismic data acquired by at least one of saidseismic acquisition units.
 18. The method of claim 17, wherein thetransmitted signal received by the receiving station includes seismicdata acquired by a plurality of said seismic acquisition units.
 19. Themethod of claim 1, wherein each seismic acquisition unit has a radiotransmission range.
 20. The method of claim 19, wherein at least twoseismic acquisition units fall within the radio transmission range ofanother seismic acquisition unit.
 21. The method of claim 19, whereinthe radio transmission range of each seismic acquisition unit isomnidirectional.
 22. The method of claim 19, wherein the radiotransmission range of at least one of the seismic acquisition units isomnidirectional.
 23. The method of claim 19, wherein the radiotransmission range of at least one of the seismic acquisition units isunidirectional.
 24. The method of claim 13, wherein the transmissionchain is comprised of a plurality of seismic acquisition units.
 25. Themethod of claim 24, wherein said transmission chain includes eachseismic acquisition unit in the array.
 26. The method of claim 19,further comprising the step of adjusting the transmission range of aseismic acquisition unit so as to alter the number of other seismicacquisition units within radio transmission range of the adjustedseismic acquisition unit.
 27. The method of claim 13, wherein saidreceiving station is within short range radio range of at least twoseismic acquisition units.
 28. The method of claim 13, wherein saidreceiving station is within short range radio range of at least threeseismic acquisition units.
 29. The method of claim 18, wherein saidreceiving station transmits control signals to said seismic acquisitionunits and said control signal is transmitted over the same transmissionchain utilized to transmit seismic data from seismic acquisition unitsto the receiving station.
 30. The method of claim 18, wherein saidreceiving station transmits control signals to said seismic acquisitionunits and said control signal is transmitted over a differenttransmission chain than that utilized to transmit seismic data fromseismic acquisition units to the receiving station.
 31. The method ofclaim 13, wherein the transmissions from said seismic acquisition unitsto the receiving station are made utilizing different transmissionchains.
 32. The method of claim 13, further comprising the step ofutilizing a long range transmission to transmit control signals fromsaid receiving station to said seismic acquisition units.
 33. The methodof claim 1, further comprising the step of utilizing a long rangetransmission to transmit control signals from said control station tosaid seismic acquisition units.
 34. The method of claim 1, wherein atransmission from a seismic acquisition unit includes informationidentifying the position of the seismic acquisition unit.
 35. The methodof claim 1,wherein a transmission from a seismic acquisition unitincludes information identifying the identity of the seismic acquisitionunit.
 36. The method of claim 13, wherein said transmission path ispreset among the seismic acquisition units.
 37. The method of claim 36,wherein a second alternate transmission path is preset among the seismicacquisition units.
 38. The method of claim 13, wherein multipletransmission paths are identified.
 39. The method of claim 38, furthercomprising the step of selecting a transmission path among the multipletransmission paths prior to transmitting.
 40. The method of claim 1,further comprising the step of generating a beacon signal from at leastone of said seismic acquisition units.
 41. The method of claim 13,further comprising the step of determining the number of other seismicacquisition units within transmission range of a seismic acquisitionunit.
 42. The method of claim 13, further comprising the step ofdetermining the signal strength for other seismic acquisition unitswithin transmission range of seismic acquisition unit.
 43. The method ofclaim 13, further comprising the step of generating a beacon signal andtransmitting the beacon signal along the transmission path.
 44. Themethod of claim 43, further comprising the step of verifying thetransmission path by generating a beacon signal.
 45. The method of claim43, further comprising the step of utilizing said beacon signal toestablish a synchronized recording time among the seismic acquisitionunits.
 46. The method of claim 43, further comprising the step ofsimultaneously initiating recording of seismic data by said seismicacquisition units.
 47. The method of claim 43, wherein seismic datatransmitted from a seismic acquisition unit is time stamped.
 48. Themethod of claim 1, wherein each acquisition unit has a set of antennaparameters associated therewith and an adjustable transmission range,the method further comprising the step of adjusting the transmissionrange by adjusting the transmission parameters.
 49. The method of claim1, wherein each acquisition unit has a set of antenna parametersassociated therewith and an adjustable transmission direction, themethod further comprising the step of adjusting the transmissiondirection by adjusting the transmission parameters.